1. Field of the Invention
The present invention relates to a perpendicular magnetic recording type magnetic read/write apparatus and a perpendicular magnetic recording medium used in this apparatus.
2. Description of the Related Art
In improving magnetic recording density, it is beginning to prove difficult to reduce the medium noise while improving the thermal decay resistance.
One solution to this problem is to use a magnetic film medium whose magnetic anisotropic energy has been increased by means of a suitable material. However, if a material having an increased magnetic anisotropic field is used to increase the magnetic anisotropic energy of the magnetic film medium, a recording head cannot perform write operations well. On the other hand, if a material having a large saturation magnetization is used without increasing the magnetic anisotropic field, the magnetostatic action increases, making noise reduction difficult.
Meanwhile, a perpendicular magnetic recording system which records magnetization perpendicularly has been conventionally studied. In this system, unlike in longitudinal magnetic recording, no demagnetizing field from an adjacent bit acts on the magnetization transition region. Conversely, an adjacent bit helps stabilize magnetization in the magnetization transition region. Therefore, this perpendicular magnetic recording system is stable under a high-density recording conditions and hence is considered to be advantageous in high-density recording. Recently, this perpendicular magnetic recording has also come to be regarded as advantageous in thermal decay resistance, since a high resolution can be maintained even with a large film thickness compared to a longitudinal magnetic recording medium. Therefore, perpendicular magnetic recording is also beginning to attract attention in this respect. However, it is reported that in perpendicular magnetic recording, at a low-density, bits are strongly influenced by an internal demagnetizing field as a result of the thin film shape effect, so reduction of the read output is greater at low density. Accordingly, even in perpendicular magnetic recording it is necessary to study the thermal decay resistance.
Much as in a longitudinal magnetic recording medium, increasing the anisotropic energy of a magnetic film is effective in a perpendicular magnetic recording medium. However, this makes the writing of data by a head difficult. In addition, if the size of the magnetic grains of a perpendicular magnetic recording medium is decreased to reduce the transition noise, noise in the saturation magnetization region increases. This makes it difficult to increase the signal to medium noise ratio S/Nm itself.
The present invention has been made to solve the above problems, and has as an object the provision of a perpendicular magnetic recording medium having a high thermal decay resistance of magnetic film grains and a high signal to medium noise ratio S/Nm.
A magnetic recording medium of the present invention comprises a substrate and a perpendicular magnetic layer formed on the substrate,
wherein the magnetic recording medium has magnetic characteristics by which an anisotropic magnetic field Hk and a saturation magnetization Ms satisfy the condition 2 less than Hk/4xcfx80Ms less than 5 . . . (1), letting xcex1 be the inclination of a hysteresis curve representing a change in magnetization M when a magnetic field H is applied in a direction perpendicular to the perpendicular magnetic layer, the anisotropic magnetic field Hk, the saturation magnetization Ms, and a coercive force Hc satisfy the condition 0.01 less than {(xcex1xe2x88x921)Hc+4xcex1Ms}/Hk less than 0.2 . . . (2), and a longitudinal residual magnetization Mr is less than 0.2 times the saturation magnetization Ms.
A magnetic read/write apparatus of the present invention comprises
a magnetic recording medium,
a driving means for supporting and rotating the magnetic recording medium, and
a recording head which writes and reads data to and from the magnetic recording medium,
wherein the magnetic recording medium comprises a perpendicular magnetic layer, and has magnetic characteristics by which an anisotropic magnetic field Hk and a saturation magnetization Ms satisfy the condition 2 less than Hk/4xcfx80Ms less than 5 . . . (1), letting xcex1 be the inclination of a hysteresis curve representing a change in magnetization M when a magnetic field H is applied in a direction perpendicular to the perpendicular magnetic layer, the anisotropic magnetic field Hk, the saturation magnetization Ms, and a coercive force Hc satisfy the condition 0.01 less than {(xcex1xe2x88x921)Hc+4xcfx80Ms}/Hk less than 0.2 . . . (2), and the longitudinal residual magnetization Mr is less than 0.2 times the saturation magnetization Ms.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.